The invention relates to amino-siloxane compositions and their use as carbon dioxide absorbent materials.
Pulverized coal power plants currently produce over half the electricity used in the United States. In 2007, these plants emitted over 1900 million metric tons of carbon dioxide (CO2), and as such, accounted for 83% of the total CO2 emissions from electric power generating plants and 33% of the total U.S. CO2 emissions. Eliminating, or even reducing these emissions, will be essential in any plan to reduce greenhouse gas emissions.
Separating CO2 from gas streams has been commercialized for decades in food production, natural gas sweetening, and other processes. Aqueous monoethanolamine (MEA) based solvent capture is currently considered to be the best commercially available technology to separate CO2 from exhaust gases, and is the benchmark against which future developments in this area will be evaluated. Unfortunately, amine-based systems were not designed for processing the large volumes of flue gas produced by a pulverized coal power plant. Scaling the amine-based CO2 capture system to the size required for such plants is estimated to result in an 83% increase in the overall cost of electricity from such a plant. Applying this technology to all existing pulverized coal power plants in the U.S. could cost $125 billion per year, making MEA-based CO2 capture an undesirable choice for large-scale commercialization.
There are many properties that desirably would be exhibited, or enhanced, in any CO2 capture technology contemplated to be a feasible alternative to the currently utilized MEA-based systems. For example, any such technology would desirably exhibit a high net CO2 capacity and elimination of the carrier solvent (for example water), and could provide lower capital and operating costs (less material volume required to heat and cool, therefore less energy required). A lower heat of reaction would mean that less energy would be required to release the CO2 from the material. Desirably, the technology would not require a pre-capture gas compression, so that a high net CO2 capacity could be achieved at low CO2 partial pressures, lowering the energy required for capture. Technologies utilizing materials with lower viscosities would provide improved mass transfer, reducing the size of equipment needed, as well as a reduction in the cost of energy to run it. Low volatility and high thermal, chemical and hydrolytic stability of the material(s) employed could reduce the amount of material needing to be replenished. Of course, any such technology would also desirably have low material costs, so that material make-up costs for the system would be minimized. The operability of CO2 release at high pressures could reduce the energy required for CO2 compression prior to sequestration. Finally, such technologies would also desirably exhibit reduced corrosivity to help reduce capital and maintenance costs, and further would not require significant cooling to achieve the desired net CO2 loading, reducing operating costs.
Unfortunately, many of the above delineated desired properties interact and/or depend on one another, so that they cannot be varied independently. Trade-offs are therefore required. For example, in order to have low volatility, the materials used in any such technology typically must have a relatively high molecular weight. However, in order to achieve low viscosity, the materials must typically have a relatively low molecular weight. Moreover, in order to achieve high CO2 capacity at low pressures, the overall heat of reaction of the absorbent material with carbon dioxide (to form an adduct comprising structural units derived from the absorbent material and CO2) should be relatively high. However, the ease of regeneration of the absorbent material and carbon dioxide from the adduct would benefit from a relatively low heat of reaction.
Therefore there is a need for a CO2 capture technology that optimizes as many of the above desired properties as possible, without causing substantial detriment to other desired properties. At a minimum, in order to be commercially viable, such technology would desirably be utilized at a relatively low cost, and would also utilize materials(s) having low volatility, high thermal stability, and a high net capacity for CO2.